In recent years, solid-state light illuminators, such as LASERs and light-emitting-diodes (LEDs), have drawn attention as alternative light sources to traditional light sources, such as arc lamps, for use in display systems due to many advantages, such as compact size, greater durability, longer operating life, and lower power consumption. As a way of example, FIG. 1 diagrammatically illustrates a typical display system using solid-state light sources.
Referring to FIG. 1, illumination system 102 has multiple solid-state illuminators for providing light of different colors. The light is directed to light valve 104, such as a spatial light modulator, that modulates the incident light based on image data 114, such as bitplane data. The bitplanes are derived from desired images 106 based on the output of color mapping table 110, which converts input pixel data into output pixel data associated with a pre-determined sequence of color duty cycles. The sequence of duty cycles often has more colors than the colors provided by the illuminators of the display system by overlapping the ON-time of the illuminators so as to get the most from the illuminators as possible. As a consequence, the full-on white can be increased through overlapping of on-time of the illuminators. In one example, assuming the input to the color mapping table can be pixel data for red, green, and blue colors, the output of the color mapping table can have pixel data for red, green, blue, yellow, cyan, magenta, and other suitable colors or bands of wavelengths, such as white light.
Based upon the output pixel data from the color mapping table, bitplanes 114 are derived. At a time when a particular color of light (e.g. red color) illuminates the light valve, the corresponding bitplane is used to determine the states of individual pixels of the light valve while the time duration of the states is determined by the bitplane weight. The modulated light is projected onto a display target so as to produce the color image component. The calorimetric properties of the produced color image component on the display target are thus determined by the bitplane and the color of the light illuminating the light valve. However, the produced color image component on the display target may not have consistent calorimetric properties due to variations of the solid-state light illuminators.
It has been observed that, regardless of the widely embraced superior properties over traditional light sources, solid-state light illuminators, such as LEDs may suffer from calorimetric variations due to environment changes. Specifically, the light emission intensity of a typical solid-state light illuminator may vary with the temperature changes of the light emitting element even with fixed electronic current. On the other hand, the color mapping table (110), such as the a three-dimensional lookup as implemented in BrilliantColor™ is often built for a “golden” set of parameters including a choice of duty cycles, specific illuminators, and electronic current levels used for driving the specific illuminators. Changes in duty cycles, illuminators, or electronic current levels will cause output colors from the color mapping table offset from their “ideal” values that correspond to the “golden” set. For example, a variation in the duty cycle of the illuminators will cause changes in the duty cycles of color light illuminating the spatial light modulator, which in turn, results in variations of the colors of the produced images on the screen.